Cactus Biogeography: A Prickly (Pear) Problem for Young Life Creationism

Young-earth creationists (YECs) routinely appeal to post-flood hyper-evolution to explain the diversification of pairs of ancestral animals into dozens and even hundreds of descendant species in the space a few hundred years following a global flood 4500 years before present.  For example, a pair of ancestral canines are said to have evolved in less than 1000 years into over 100 descendant species including all fox and wolf species alive today or even more dramatically, a pair of ancestral finch-like birds has been proposed to have evolved into over 1500 species of finches (see: Avian Ark Kinds). I call this explanation of modern-day biological diversity Young Life Creationism (YLC).

I have addressed this rapid speciation hypothesis many times (see my YEC hyper-evolution archive for other articles) but it occurred to me that most of the attention is paid to land animals because their preservation is a focal point of the flood account in Genesis.  However, we might ask, what do YECs expect to observe with respect to the history of species of plants?  Have plants also experienced massive recent diversification into many species as well?  

Plants were not specifically recorded as being preserved on Noah’s Ark. It is assumed that they would have had to fend for themselves when the world was supposedly covered with water.  YECs presume that plants would have survived as pieces of vegetative matter and seeds that then repopulated the world with plants following the recession of the flood waters. 

For YECs, unlike air-breathing land animals which experienced the most extreme bottleneck possible—a restriction to two individuals in many cases—plants, insects, fungi, bacteria, etc.. would not be expected to have been stripped of their genetic and species diversity during the flood. YECs therefore should expect to observe stark differences in the geographic distribution and patterns of genetic diversity of these organisms.

Focusing on plants what should we expect to see if they survived the flood simply by floating on the water?

We would expect to see the same kinds of plants distributed over the whole world where climatic conditions are comparable. For example, southern Africa and southern California and Mexico have similar climates and soil types and so we would expect that the same or very similar species of plants should have adapted to live in those locations. The tropical jungles of Africa and South America should be filled with the same or at least very similar species..  

But what do we observe? We observe that there is great geographical heterogeneity with respect to the type of plants that we see. The kinds of plants found in South Africa are very different from those found in Southern California and Mexico.  The tropics of Africa are filled with plants unrelated to those found in South America? The differences are not a matter of different species but wholly different plants altogether inhabit these locations.  It is as if all members of the cat family were only found in South Africa and all canines were only found in California.  Why should this be if a global flood mixed up the seeds and plants material present in the pre-flood world?   

Let’s look at one example to illustrate this unexpected geographical pattern of plants: the cacti.

Cacti are a New World Plant

The term cactus refers to members of a species-rich family, or possibly several families, of plants. There are 1750 recognized living species of cacti.  Those species are further divided into 127 genera which are groups of species with similar features.  Some examples of genera include: Opuntia (prickly-pears), Carnegiea (Saguaros) and Schlumbergera (Christmas cactus).  Each of these genera have tens to hundreds of species. Most are stem succulents—having thickened stems for water storage—and have multiple adaptations to living in dry habitats, but many are epiphytes and live in tropical portions of South America.

It may surprise you to learn that cacti are only found in the New World.* The 1700+ species of cacti live in South and North America, the Caribbean islands and the Galapagos Islands.  In contrast to the New World, arid regions of Asia and Africa are devoid of cacti.  South Africa is home to thousands of species of spiny, stem-succulent plants that living in environments very similar to those that cacti inhabit in the New World but they are not cacti. Many belong to an entirely unrelated family of 7500 species of plants known as the Ephorbiaceae or spurge family.

This should strike the global flood advocate as a strange and unexpected geographic pattern. Why should more than 1700 cactus species be restricted to the New World if cacti existed before a global flood and passed through that flood as fruits—called “pears”—or seeds?  How come the cacti only seem to have survived in the New World?

Furthermore, why have no fossils of a cactus in presumed global flood rocks ever been found if they existed prior to the flood?

Are all cacti members of the same created “kind” of plant or are individual genera of cacti the original created units?

Before we can assess the YEC dilemma we need to take a look at how they define a “kind.”

Ken Ham and his staff at Answers in Genesis claim that all the species included in a single kind are the products of common ancestor created directly by God during the 6 days of creation.  That then begs the questions, just what is a “kind?” How a kind corresponds to modern taxonomic groups has been a source of much discussion among “baraminologists”—the term for creationist taxonomists—but they generally agree that a “kind” is roughly equivalent to the taxonomic designation of “family,” though no formal definition has ever been produced.  Examples of animal families are the canines, felines, great apes etc…

What about plant kinds?  There is far less speculation among YECs about plant kinds but the few authors that have ventured into talking about plants tend to see plant kinds as either represented by genera or families.  What about cacti?  There is very little in the creationist literature about cacti but Todd Elder, a self-described “baraminologist” who has sought to identify how many created kinds there are in the world, accepts that kinds of plants are equivalent to families and he places all cacti in a single kind.  http://www.baraminology.net/plantae/angiosperm/ He places all 300,000 flowering plant species into just 365 kinds which amounts to an average of 831 species per kind.  Presumably most or all of these species would have evolved from the original 365 representatives of their kinds in just over 6000 years.

Dr. Todd Wood is the only YEC that I have found that has explicitly discussed cacti (Wood 2005 and Wood and Garner, 2009). In particular he addresses one of the many types of cacti, the Opuntia or prickly pear cacti. He has made the case that the all of the species of prickly pear cacti on the Galapagos Islands are descendants of what was likely a single species of prickly pear that dispersed to the islands from a population in South America.  He believes all of the prickly pear cacti species are members of the same kind and have a common ancestor. They have evolved into the species we see today by natural selection and genetic alterations (mutations).

I don’t know if most YECs believe that cacti are all just one big family bound by a single common ancestor or if they think that most genera of cacti are so different that they belong to separate “kinds” and therefore were created as many separate kinds.  Regardless, both scenarios present a difficult task for the YEC apologist.

Pick your poison: Ultra-fast expansive evolution or wildly unlikely biogeographic distribution

Option 1: Ultra-fast evolution: One possible YEC explanation for the observation that the cacti family has a New Word distribution is that all cacti are the descendants of a single or small number of common ancestors of a single species that survived a global flood.  Those survivors happened to find themselves in the New World and they evolved (or YEC term: diversified or devolved) into all 1700+ species in 127 genera that are alive today.

All of this evolution would have had to have happened in just a few hundred years, starting not more than 4500 years ago. Considering the incredible amount of genetic, morphological and habitat differences within the cactus family, this is an astounding amount of evolution.  Looking at gene trees which show the amount of genetic divergence of cacti.  When compared to that of similar trees of the canines and felines it is apparent to me that the cacti are far more genetically diverse those two families.  In fact, two “cacti” may be as distinct genetically as two carnivores such as a cat and a dog are from one another. 

Option 2: Many different kinds and an incredible coincidence: Some YECs may not feel comfortable invoking massive amounts of evolution to explain all the diversity of the larger cacti family and choose to define the original “kinds” to be equivalent to that of genus or maybe subfamily.  For example, maybe the saguaro and prickly pear cacti are different kinds meaning they were created separately by God.  The cactus family may just be a larger grouping of 50 to 127 different “kinds” of plants, much like the YEC would say that the term primates refers to a grouping of many different “kinds” of primates such as great apes, new world monkeys and lemurs which all share similar design features even though they don’t share a common ancestor.

However, splitting the cacti into many different kinds creates (pun intended) a perplexing problem. If God created 100 or more different cacti kinds in the creation week how did a global flood sort out the remains of all those different kinds such that they were only preserved in the New World?

Adding to this problem is the observation that no fossil of a cactus has ever been found in a global flood rock deposit.**  There is no reason to believe that cacti wouldn’t have been well preserved under the conditions that global flood advocates propose.  So the lack of any cactus fossil is rather curious.  YECs could counter that before the flood there were no deserts and so the needles of cacti had not yet appeared but this would require that many different kinds of cacti all lacked needles and then they all evolved needles after the flood in addition to them only being preserved in the New World. But this only raises more questions such as how was the genetic ability to make needles preserved in plants before the Flood while they were reproducing and experiencing great genetic sorting each generation?

It’s not just cacti

Cacti aren’t the only plants that have this distinct biogeographic distribution. There are many other plant families and genera that are found solely on one or a few continents to the exclusion of others.  Focusing solely on the New World, there are several other families of plants (eg. Calyceraceaea, 60 species; and Burnelliaceae, 230 species) found only in South America. There are hundreds of genera of plants that are only found in the New World. For example the genus Yucca includes 40 to 50 species that are found only in North America and down to Guatemala.  This genus includes one of my favorite species of desert plants—the Joshua trees—but also includes several cultivars that are familiar to most people.

Why are YECs attracted to speculating about post-flood hyper-evolution?

I suggested that YECs have to pick their poison with respect to cacti.  The poison they are most likely to pick is #1.  YECs have greatly expanded their definition of “kind” to include greater and greater morphological and genetic diversity of species and so including 1700+ species into a single kind would not be surprising.  Hyper-evolutionary processes following a global flood has become the go-to YEC “explanation” for the vast biological diversity we observe today. To some extent, it has also become a way to explain (or explain away) the uneven distribution of plant and animal groups across continents.

The fact that so many plant groups are restricted to a single continent or island (Hawaii contains many unique flowering plant families) makes it very difficult for the YEC to contend that God created each species or even each genus of plant separately because it would be difficult to explain how groups of plants we identify as having overall similarities might be found together after experiencing the chaotic waters of a global flood. Hence, YECs have found it helpful to think of large groups of species as being the products of a small number of common ancestors present after a global flood.

For land animals, one strong impetus for appealing to post-flood hyper-evolution is the lack of space on Noah’s Ark to contain representatives of all land animal species or even genera. By having a broad definition of a “kind” they can hypothesize (though they never test their hypothesis) that only a single pair of animals represented all 100+ canine species that have lived after the global flood.

On the surface, plant diversity wouldn’t appear to require the same hyper-evolution after the flood because presumably every species God created in the beginning could have survived the flood.  But as we have seen, the biogeographic patterns of genus and family distribution on the post-flood earth provides a reason for YECs to propose that plants also were also decimated by the flood, leaving a small number to speciate via hyper-evolutionary mechanisms, thus far not clearly identified or investigated , into the hundreds of thousands of species that we enjoy today.

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*There is one cactus that lives in Africa. This plant is a member of a genus of cacti that is found in South America and is very closely related to them (see Calvente et al. 2011). The plant is a polyploid which means it has doubled its chromosome count and is an epiphyte. The very close relationship to plants in South America and to one diploid species in particular strongly suggests it has only recently migrated from South America to the New World either by bird or possibly not long ago by human agency.  For our purposes here there is no doubt that this plant had its origins in South America and was recently introduced to the Old World and so is not native to the Old World.

**There is one fossil of a cactus, a prickly-pear, from the Green River formation rocks in Wyoming.  The origin of these rocks are highly disputed in the YEC literature. Some say they were produced during a global flood others believe they are post-flood deposits.  At this time it seems that the post-flood hypothesis is more widely accepted which is why I say that there are no cactus fossils in global flood rocks.

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Calvente, Alice, Daniela C. Zappi, Félix Forest, and Lúcia G. Lohmann. “Molecular phylogeny of tribe Rhipsalideae (Cactaceae) and taxonomic implications for Schlumbergera and Hatiora.” Molecular Phylogenetics and Evolution 58, no. 3 (2011): 456-468. http://www.sciencedirect.com/science/article/pii/S1055790311000029

Hernández-Hernández, Tania, Héctor M. Hernández, J. Arturo De-Nova, Raul Puente, Luis E. Eguiarte, and Susana Magallón. “Phylogenetic relationships and evolution of growth form in Cactaceae (Caryophyllales, Eudicotyledoneae).” American journal of botany 98, no. 1 (2011): 44-61.

Griffith, M. Patrick, and J. Mark Porter. “Phylogeny of Opuntioideae (Cactaceae).” International Journal of Plant Sciences 170, no. 1 (2009): 107-116.

Hernández-Hernández, Tania, Héctor M. Hernández, J. Arturo De-Nova, Raul Puente, Luis E. Eguiarte, and Susana Magallón. “Phylogenetic relationships and evolution of growth form in Cactaceae (Caryophyllales, Eudicotyledoneae).” American journal of botany 98, no. 1 (2011): 44-61. http://www.amjbot.org/content/98/1/44.full.pdf+html

Wood, Todd Charles. A creationist review and preliminary analysis of the history, geology, climate, and biology of the Galápagos Islands. Vol. 1. Wipf and Stock Publishers, 2005.

Wood, Todd Charles, and Paul A. Garner, eds. Genesis kinds: Creationism and the origin of species. Vol. 5. Wipf and Stock Publishers, 2009.

Editing provided by LC